1. Field of the Invention
This invention relates to a filter device for filtering air that is to be breathed through a tracheostoma, for example in patients who have received a tracheostomy, for example as part of a laryngectomy. Under such circumstances, the device can be fitted over a tracheostoma, body worn, for example directly over a tracheostoma, or to a tracheostomy tube, and serves to simulate some of the functions of the nose. The device can include a valve to assist in diverting the flow of exhaled air, for example to permit speech.
2. Description of Related Art
A tracheostomy is a surgical procedure in which an opening is formed through the anterior surface of the neck into the trachea. The opening is referred to as a tracheostoma. A tracheostomy tube can be provided to extend between the tracheostoma and the trachea.
A laryngectomy is a surgical procedure, used for example to treat a carcinoma, which involves removal of the larynx or voice box and creation of a tracheostoma. A consequence of the procedure is that the trachea is no longer connected to the pharynx but is diverted to the tracheostoma. After this procedure, normal nasal function is not possible.
In a subject whose breathing functions normally, the nose and the mucous membrane lining of the nasal cavity perform important functions in conditioning inhaled air. The convoluted passages and rich blood supply serve to increase both the temperature and humidity of the inhaled air to minimise the differential in these parameters with those of the surface of the lungs. Normally some heat and moisture is also captured from exhaled air prior to its release to the atmosphere. The mucous lining of the nasal passages also serves to remove particulate matter, such as fine dust particles, pollutants and micro organisms, from the inhaled airstream, and the action of cilia transports mucous and any particles away from the lungs.
The exchange of heat and moisture, and filtration are clearly beneficial to the patient and, in their absence, clinical consequences such as increased incidence of chest infections, elevated levels of secretion production and encrustation are observed.
The upper airways also provide resistance to air flow which promotes good thoracic muscle tone and allows good respiratory function to be maintained.
A further consequence of a laryngectomy is that speech is no longer available by the normal method of passage of air through the vocal cords of the larynx. Where clinical conditions permit, it is clearly in the patient's interest to restore the facility of speech.
It is sometimes possible to insert a voice prosthesis in an artificially created fistula between the upper regions of the trachea and the oesophagus. It then becomes necessary to provide means for directing the flow of exhaled air through the voice prosthesis. This can be conveniently achieved by the incorporation of a valve in an externally worn device.
When a patient has received a tracheostomy, in effect all inhaled air enters the lungs via the tracheostoma, and the nose is effectively not involved in the inhalation process. Exhaled air may pass through the tracheostoma or, if a voice prosthesis has been fitted, the stoma can be occluded so that the exhaled air is diverted through the voice prosthesis into the pharynx and the mouth, enabling the patient to speak. It is desirable that the flow of the exhaled air be controlled by means of a tracheostoma valve. In these situations, the valve can be arranged to remain open during breathing but, with a small additional increase in exhaled air pressure, can be closed to divert the air flow.